Unless I am wearing a t-shirt of some sort, I wear an undershirt with everything else.
As to wife beater, I know far more people who will know exactly what I am talking about if I say wife beater, A Shirt would have them returning a blank stare.
O.K. This may be a stupid question, but what's the difference between an A-Shirt and a Wife Beater. I thought they were the same thing? Never mind. I now see it's been covered.
And for the record - usually a T-shirt, but sometimes an A-shirt or a muscle shirt in the summer.
I wear t-shirts under cardigans or button-up shirts that I wear open in the winter. But I can't wear them otherwise. They tend to make me hot or uncomfortable.